The invention relates to improvement of the quality of a radiographic image of an object obtained by a radiographic X-ray unit containing an anti-diffusion or anti-scatter grid.
The invention applies advantageously but not exclusively to mammography examinations for the detection of micro-calcifications inside a breast.
A radiographic X-ray unit, used in particular in mammography, is equipped with an anti-diffusion grid arranged between the object to be radiographed, in this case a breast, and a receiver of radiographic images, for example a CCD (charge-coupled) receiver. In conventional fashion, the anti-diffusion grid is composed of a series of plates that are all directed toward the focal point of X-ray radiation emitted in the direction of the object and of the image receiver. Thus, the anti-diffusion grid allows the undiffused direct beams to pass, while the diffused beams are absorbed by the plates.
This being so, the resolution of the image receiver is generally finer than the space between two plates, which typically is of the order of 0.3 mm. The result of this is that the plates are visualized on the radiographic image obtained, which is particularly troubling in mammography because it makes detection of micro-calcifications more difficult.
One solution of this problem consists of displacing the grid during exposure, in rectilinear translation in its plane, i.e., substantially perpendicular to the plates of the anti-diffusion grid. Such translation may be effected only in one direction or, in alternating fashion, in both directions.
The quality of the image is thus improved but nevertheless remains inadequate. In addition, generation of an alternating movement is a mechanically more complicated solution.